Currently under research and development are processing methods for improvement in density and miniaturization in production of ULSI semiconductor devices. One of the methods, chemical mechanical polishing (CMP) technology, is now a technology essential in production of semiconductor devices, for example, for smoothening of an interlayer dielecrtric film, forming a shallow trench device isolation, and forming plugged and embedded metal wiring.
In production of semiconductor devices, inorganic insulation film layers such as a silicon oxide insulation film are formed by methods such as plasma CVD and low-pressure CVD. Polishing slurries of fumed silica are commonly studied as a conventional chemical mechanical abrasive in state of slurry for use in smoothening the inorganic insulation film layer. The fumed silica polishing slurries are produced by grain growth, for example, by oxidative thermolysis of tetrachlorosilane and subsequent pH adjustment. However, such a fumed silica polishing slurry still has a problem that the polishing speed is lower.
A shallow trench isolation method has been used for isolation of elements in an integrated circuit in devices in the generation of a design rule of 0.25 μm or later. In the shallow trench isolation method, CMP is used for removal of excessive silicon oxide films formed on a substrate, and a stopper film smaller in polishing speed is formed under the silicon oxide film for termination of polishing. For example, silicon nitride is used for the stopper film, and the difference in polishing speed between the silicon oxide film and the stopper film is preferably greater. However, colloidal silica-based polishing slurries have a smaller polishing speed ratio between the silicon oxide film and the stopper film at approximately 3, and thus, do not have properties practically usable for shallow trench isolation.
On the other hand, cerium oxide polishing slurries have been used as abrasives for use on the surface of glasses such as of photomask and lens. Cerium oxide particles are softer than silica or alumina particles, less likely to cause scratching on the polishing surface, and thus, useful for finishing mirror-surface polishing. The particles also have an advantage that the polishing speed therewith is faster than that of silica polishing slurries. Recently, CMP polishing slurries for semiconductor processing containing a high-purity cerium oxide polishing powder have been used. (See Japanese Patent Application Laid-Open No. 10-106994.
A water-soluble polymer having a hydrophilic carboxyl or carboxyl salt group is known to be added as an additive to the cerium oxide CMP polishing slurry for control of the polishing speed of a cerium oxide CMP polishing slurry and improvement of global smoothness (see, for example, Japanese Patent No. 3,278,532).
Examples of monomers for the additive include an acrylic acid, an itaconic acid, a maleic acid, and the salts, and the most polymerizable acrylic acid is seemingly most preferable. However, cerium oxide CMP polishing slurries containing an additive of water-soluble polymer as the monomer could not reduce the difference in residual film thickness due to the pattern density difference of the film to be polished sufficiently.
There are fewer studies on methacrylic acid polymers, because a methacrylic acid is more hydrophobic and only soluble in water at a concentration of 18% at room temperature and hardly gives a high-molecular weight polymer by polymerization. Accordingly, it is not regarded as a monomer suitable for the polymer for use as the additive.